//#include<stdio.h>
////#define WIN 1
//int main()
//{
//#ifdef WIN
//	printf("haha\n");
//#endif
//
//#ifdef WIN
//		printf("hehe\n");
//#endif
//	return 0;
//}

//#include<stdio.h>
//#define WIN 1
//int main()
//{
//#if !defined WIN
//	printf("hehe\n");
//#endif
//
//}


//#if 0
//int main()
//{
//	printf("hehe\n");
//	return 0;
//}
//#endif
//
//#include<stdio.h>
//int main()
//{
//
//}

#include<stdio.h>
void MissingNumber(int* nums, int N)
{
	int i = 0;
	int sum = 0;
	for (i = 0; i < N; i++)
	{
		sum ^= nums[i];
		sum ^= i;
	}
	sum ^= i;
	printf("%d\n", sum);
}
int main()
{
	int arr[9] = { 0,1,2,3,4,5,7,8,9};
	MissingNumber(arr, 9);
}